MICROFILTRATION OF MILK WITH CERAMIC MEMBRANES - INFLUENCE ON CASEIN COMPOSITION AND HEAT-STABILITY

Skim milk was microfiltered through ceramic membranes with pore sizes 1.4 or 0.8 mu under uniform transmembrane pressure. The permeates and retentates collected were analysed for total solids, whey proteins and caseins. The casein composition was studied by anion-exchange chromat ography and the mean average diameter of the micelles was measured by photon correlation spectroscopy. Microfiltration resulted in fractiona tion of the casein micelles; large micelles were retained in the reten tate. This separation affected the casein composition of the permeates and retentates. Heat stability studies showed that the permeates were more stable than the retentates or the source skim milk. These differ ences were largely the result of lower total solids (TS) content in th e permeates because adjustment of the TS to 9% offset the improvement. Nevertheless, changes in the micelle size distributions in the retent ates played a role in the heat stability of the latter fraction. The r etentates were less stable than the respective permeates at the unadju sted pH, even after adjustment of the TS level to 9% whereas they were more stable in the region of the minimum of the heat coagulation time (HCT)-pH profile.